Photographic reversal process employing organic mercaptan compounds

ABSTRACT

This disclosure relates to a rapid reversal photographic process. The process comprises the steps of (1) contacting a copy medium comprising a metal image pattern and a metal ion image pattern with an organic mercaptan compound to form insoluble metal mercaptide salts in the areas corresponding to the metal ion image pattern, and (2) contacting the copy medium with a photographic bleaching agent to oxidize the metallic image to soluble salts. The soluble salts may then be dissolved out or fixed by contacting with a suitable solvent or photographic fixing or stabilizing solution. The process in a preferred embodiment comprises the steps of (1) exposing a photosensitive copy medium imagewise to a source of radiation to provide a negative latent image, (2) developing the copy medium to provide a negative metallic image in the exposed portions of the copy medium, (3) contacting the copy medium with an organic mercaptan compound to form insoluble metal mercaptide salts in the nonexposed areas of the copy medium, (4) contacting the copy medium with a photographic bleaching solution to reoxidize the metallic image in the exposed portions of the copy medium to soluble salts and (5) contacting the copy medium with a photographic fixing solution to dissolve the soluble salts from the exposed portions of the medium. The photosensitive medium may, for example, be a photographic silver halide emulsion or a photoconductor such as titanium dioxide dispersed in a binder.

United States Patent Gallet et al.

[ 1 Feb. 8, 1972 [54] PHOTOGRAPHIC REVERSAL PROCESS EMPLOYING ORGANIC MERCAPTAN COMPOUNDS [72] Inventors: Jacques Henri Gallet, Arlington; Robert Francis Gracia, Scituate, both of Mass.

[52] US. Cl. ..96/59, 96/48, 96/27 R, 96/1 LY, 96/1.5, 250/65 T [51] Int. Cl ..G03c 5/50 [58] Field ofSearch ..96/1, 1 LY, 1.5, 59; 117/37 LX [56] References Cited UNITED STATES PATENTS 3,210,189 10/1965 Wartburg..... .96/59 3,384,485 5/1968 Blake 96/59 X 3,390,989 7/1968 Berman et a1... .....96/1 X 3,414,410 12/1968 Bartlett et a1. ..96/1 X 3,471,288 lO/l969 Berman ......96/l

OTHER PUBLICATIONS Henn et al., A Simple Reversal Process, Photographic Science and Engineering, Vol. 11, No. 5, Sept-Oct. 1967, pp. 363-364 Primary Examiner-George F. Lesmes Assistant ExaminerJohn R. Miller Att0mey-Homer 0. Blair, Robert L. Nathans and W. Gary Goodson [57] ABSTRACT This disclosure relates to a rapid reversal photographic process. The process comprises the steps of (1) contacting a copy medium comprising a metal image pattern and a metal ion image pattern with an organic mercaptan compound to form insoluble metal mercaptide salts in the areas corresponding to the metal ion image pattern, and (2) contacting the copy medium with a photographic bleaching agent to oxidize the metallic image to soluble salts. The soluble salts may then be dissolved out or fixed by contacting with a suitable solvent or photographic fixing or stabilizing solution.

The process in a preferred embodiment comprises the steps of (1) exposing a photosensitive copy medium imagewise to a source of radiation to provide a negative latent image, (2) developing the copy medium to provide a negative metallic image in the exposed portions of the copy medium, (3) contacting the copy medium with an organic mercaptan compound to form insoluble metal mercaptide salts in the nonexposed areas of the copy medium, (4) contacting the copy medium with a photographic bleaching solution to reoxidize the metallic image in the exposed portions of the copy medium to soluble salts and (5) contacting the copy medium with a photographic fixing solution to dissolve the soluble salts from the exposed portions of the medium. The photosensitive medium may, for example, be a photographic silver halide emulsion or a photoconductor such as titanium dioxide dispersed in a binder.

47 Claims, No Drawings PHOTOGRAPHIC REVERSAL PROCESS EMPLOYING ORGANIC MERCAPTAN COMPOUNDS BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to the field of photographic processing and more particularly, to a rapid reversal process for developing a positive photographic image.

2. Description of the Prior Art Photographic reversal effects are well known in the art and generally refer to a process which causes a latent image to develop as a positive rather than as a negative. The term has been generally employed to describe a condition resulting from extreme overexposure of negative materials, which tends to destroy the developability of the latent image and causes the image to develop as a positive rather than as a negative. Reversal by overexposure varies with different emulsions; a few commercial emulsions showing partial reversal at exposures which are of practical significance but in general, the exposures required are so much greater than those required in practice that reversal from this source is comparatively rare. Emulsions with a high percentage of iodide tend to show reversal effects at lower exposures than those of silver bromide.

Diffusion transfer reversal is a more recent process where an exposed photographic emulsion layer is developed by means of a developer that contains a silver halide solvent while it is in contact with another layer that is not light sensitive, but which is usually specially prepared. In the course of forming a negative image in the exposed layer, the developer dissolves sufficient amounts of the unexposed silver halides (representing the positive image) which are transferred to the second layer, creating a positive image on its surface by reaction of the dissolved silver halides with substances usually contained on the second support.

Thus, a positive image can be produced on a nonlight-sensitive layer simultaneously with development of a negative image in an exposed silver halide layer. Simultaneity of negative and positive image formation is not a limiting requirement, however, for if it is considered advantageous a distinct two-step procedure can be employed. A discussion of diffusion transfer reversal process can be found in Neblette, Photography, Its Materials and Processes, 5th Edition, D. Van Nostrand Co., Inc., New York, 1952.

A more recent reversal process is reported by R. W. Henn and Nancy H. King, Photographic Science and Engineering, Volume I I, No. 5, Pages 363 and 364, Sept.Oct. 1967. This process depends upon the strong adsorption of certain mercaptans, such as l-phenyl-5-mercaptotetrazole to developed silver and the resistance of the coated silver to subsequent bleaching. In this process, a photographic copying medium is exposed and developed in a conventional manner. Thereafter, the deveioped copy medium is uniformly reexposed to light and developed in a strongly alkaline hydroquinone developer containing the mercaptan. The reduction of the remaining silver halide takes place primarily in the positive image areas and is associated with adsorbed mercaptan. The negative silver is then bleached and dissolved in a blix" bath.

As will be discussed in greater detail below, the process of the invention disclosed herein is especially applicable to photosensitive mediums comprising photographic silver halide emulsions and to photosensitive materials which upon exposure can be physically developed such as photoconductors such as titanium dioxide, preferably dispersed in a binder. Silver halide emulsions are, of course, well known in the art. A copy medium comprising a photoconductor is disclosed in US. Pat. Nos. 3,380,823 and 3,l52,903. Exposure of such a copy medium to actinic radiation such as visible or ultraviolet light activates the photoconductor, rendering it capable of cffecting chemical reactions which can be utilized to develop a visible image in the medium. The photoconductor is usually dispersed throughout a support layer such as paper or plastic, or dispersed in a binder therefore, forms a photosensitive layer on a support such as paper, metal foil, plastic, glass, or the like.

As is known in'the art, the photoconductors of greatest utility for use in such copy media are compounds formed between metals and elements of group VIA of the Periodic Table, e.g., oxides, sulfides, selenides and tellurides. Preferred materials from the point of view of color, light sensitivity, ease of development and the like are titanium dioxide and zinc oxide.

The latent image of activated photoconductor formed in such copy media by imagewise exposure thereof can be suitably developed by applying image-forming materials to the media. Suitable image-forming materials include chemical redox systems, for example systems containing reducible metal ions such as silver ions or other ions of metals at least as easily reducible as ionic copper.

SUMMARY OF THE INVENTION A reversal image may be formed by the reversal process of this invention by a simple, rapid process using a copy medium that does not require special formulation or construction. Moreover, the positive image formed in a preferred embodiment by the reversal process is of high resolution and sharp image with little or no background fog. The process is rapid, requires minimum of steps and eliminates the need for substantial overexposure or reexposure.

The process comprises the steps of (l) contacting a copy medium comprising a metal image pattern and a metal ion image pattern with an organic mercaptan compound to form insoluble metal-mercaptide salts in the areas corresponding to the metal ion image pattern, and (2) contacting the copy medium with a photographic bleaching agent to oxidize the metallic image to soluble salts. The soluble salts may then be dissolved out or fixed by contacting with a suitable solvent or photographic fixing or stabilizing solution.

The photosensitive copy medium may be a conventional silver halide emulsion or a photosensitive material which upon exposure can be physically developed, such as a photoconductor, preferably dispersed in binder. In a preferred embodiment the copy medium is developed using a minimum of steps. Following exposure to an original, the copy medium is developed to provide a negative metallic image in the exposed portions of the copy medium and metal ions in the nonexposed image areas. Thereafter, the copy medium is contacted with an organic mercaptan or an alkali salt thereof. The mercaptan reacts with the metal ions in the nonexposed areas of the copy medium forming insoluble metal mercaptide salts. The mercaptan does not react with the metal image in the exposed portions of the copy medium. The next step in the process comprises contact of the copy medium with a photographic bleaching solution to reoxidize the metal to soluble salts in the exposed portions of the copy medium without affecting the mercaptides in the nonexposed areas. Finally, the copy medium is contacted with a fixer which dissolves the soluble salts in the exposed portions leaving behind thernercaptide salts in a positive image pattern.

By selection of a binder system or a separate layer for the photosensitive material of the copy medium that is a heat-sensitive composition which forms an oleophilic-hydrophilic image pattern upon selective imagewise application of heat, a planographic printing plate may be formed photographically by the process of the invention. The process would involve uniformly exposing the positive photographic image produced in accordance with the process to heat producing activating radiation which causes selective heating in the image areas, thereby producing an oleophilic-hydrophilic image pattern. The oleophilic-hydrophilic imaged printing plate so formed may then be used with a polar solvent-based ink or a greasy or oil-base ink as a printing master. Therefore, the photosensitive layer of this embodiment of this invention may be, for example, a photoconductor which becomes reversibly activated upon exposure to activating radiation such as disclosed in British Patent Specification No. 1,043,250.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred photosensitive material useful in this invention comprises a material capable of producing a physically developable image such as a photoconductor which becomes reversibly activated upon exposure to activating radiation such as disclosed in British Patent Specification No. 1,043,250 or in Belgian Pat. No. 678,170; 2may be silver halide; may be a diazosulphonate, diazothioether and/or diazocyanide such as benzenediazosulfonate and benzenediazothioether, anthraquinone sulfonate, such as 2,7-anthraquinone disulfonate, o-hydroxybenzenediazonium compounds, o-hydroxynaphthalene diazonium compounds, aromatic diazocyanides, o and p-nitromandelo nitrile, the bisulphite compounds of oand p-nitrobenzaldehyde, and inorganic complex compounds from which one or more ions or molecules are liberated by exposure: CN CNS, N SO;; 8203 NH;,, pyridine and its derivatives, and thiourea and its derivatives, which ions and molecules are bonded to at least one central metal ion, or like compound disclosed in'British Pat. Nos. 1,064,725, and 1,064,726; may be a system wherein developers and photoconductors are combined or are in separate layers, e.g., US. Pat. No. 3,152,903; methylene blue; ferric salts of organic acids such as ferric oxalate; and a mixture of mercuric chloride and ammonium or potassium oxalate (See Photographic Science and Engineering, Volume 13, Number 1, Jan.-Feb., l969,pp. 1-8.).

A preferred group of photosensitive materials are the photoconductors and especially those which are inorganic materials such as compounds of a metal with a nonmetallic element of group VIA of the Periodic Table of the Elements. Examples of such photoconductors would include oxides such as zinc oxide, titanium dioxide, zirconium dioxide, germanium dioxide, indium trioxide; sulfides such as cadmium sulfide, zinc sulfide and tin disulfide; and metal selenides such as cadmium selenide. Metal oxides are especially preferred, titanium dioxide and zinc dioxide being most preferred. Titanium dioxide having an average partical size less than about 250 millimicrons and which has been treated in an oxidizing at mosphere at a temperature of above about 200 C. and preferably between about 200 C. and 950 C. for from about 0.5 hours to about 30 hours is especially preferred, and more especially, that titanium dioxide produced by high-temperature pyrolysis of a titanium halide.

Also useful in this invention as photoconductors are certain fluorescent materials. Such materials include compounds such as silver-activated zinc sulfide, and zinc-activated zinc oxide.

While the exact mechanism by which the photoconductors work is not known, it is believed that exposure of photoconductors to activating means causes an electron or electrons to be transferred from the valence band of the photoconductor to the conductance band of the same or at least to some similar excited state whereby the electron is loosely held, thereby changing the photoconductor from an inactive form to an active form. If the active form of the photoconductor is in the presence of an electron-accepting compound, a transfer of electrons will take place between the photoconductor and the electron-accepting compound, thereby reducing the electron-accepting compound. Therefore, a simple test which may be used to determine whether or not materials have a photoconducting effect is to mix the material in question with an aqueous solution of silver nitrate. Little, if any, reaction should take place in the absence of light. The mixture is then subjected to light. At the same time, a control sample of an aqueous solution of silver nitrate alone is subjected to light, such as ultraviolet light. If the mixture darkens faster than the silver nitrate alone, that material is a photoconductor.

It is evident that the gap between the valence and the conducting band of a compound determines the energy needed to make electron transitions. The more energy needed, the

higher the frequency to which the photoconductor will respond. It is known to the art that it is possible to reduce the handgap of these compounds by adding a foreign compound as an activator which either by virtue of its atomic dimensions or by possessing a particular electronic forbidden zone structure or through the presence of traps as donor levels in the intermediate zone between the valence and the conduction band stresses the electronic configuration of the photoconductive compound, thereby reducing its band gap and thus increasing its ability to release electrons to its conduction band. Phosphors almost necessarily imply the presence of such activating substances. The effects of such impurities may be such as to confer photoconductivity upon a compound which is intrinsically nonphotoconductive. On the other hand, excessive impurity content can interfere with a compound acting as a photoconductor as above described.

The photoconductors may be sensitized to visible and other wavelengths of light by foreign ion doping, addition of fluorescent materials, and/or by means of sensitizing dyes. Bleachable dyes useful forsensitizing the photoconductors include, for example, the cyanine dyes, the-dicarbocyanine dyes, the carbocyanine dyes and the hemicyanine dyes. Additional dyes which are useful for sensitizing a photoconducting means are the cyanine dyes described on pages 371 to 429 of The Theory of Photographic Process by C. E. Kenneth Mees published by MacMillan Co. 1952.

Radiation sources which are useful for producing an initial latent image include any activating electromagnetic radiation. Thus actinic light, X-rays, or gamma rays are effective in exciting the photoconductor. Beams of electrons may also be used in place of ordinary forms of electromagnetic radiation for forming an image according to this invention.- These various activating means are designated by the term activating radiation.

The photoconductor is preferably distributed over a substrate material of sufficient strength and durability to satisfactorily serve as a carrier. Suitable materials include rag content paper, pulp paper, plastics such as polyethyleneteraphthalate and cellulose acetate, cloth, metal and glass.

The photoconductor is preferably dispersed in a binder. In general, these binders are translucent orv transparent so as not to interfere with the transmission of light therethrough. Preferred binder materials are organic materials such as resins or gelatin. Examples of suitable resins are butadiene-styrene copolymer, poly(alkyl acrylates) such as poly(methylmethacrylate), polyamides, polyvinylacetate, polyvinyl alcohol and polyvinyl pyrrolidone.

The photoconductor should be conditioned for exposure by storage in the dark for from 1 to 24 hours prior to use, by heating or by other conditioning means known to the art. After conditioning, the photoconductor is not exposed to activating radiation prior to its exposure to activating radiation for recording an image pattern. The period of exposure to form the latent image would depend upon the intensity of the light source, particular photoconductor, the type and amount of catalyst, if any, and like factors known to the art. In general, the exposure may vary from about 0.001 seconds to several minutes.

The exposed photoconductor is developed with imageforming materials comprising an oxidizing agent and a reducing agent. The oxidizing agent is generally the image-forming component of the image-forming material. The oxidizing agents comprise reducible metal ions having at least the oxidizing power of the cupric ion and include such metal ions as n A +3 p p n Pb, Cu and Cu". On contact of the metal ion with the activated or exposed portion of the photoconductor, the ions are reduced to metallic form to provide a visible image. This visible image is intensified by contact with the reducing component of the image-forming material. The reducing component is a member selected from that class of materials known in the photographic arts as physical developers. Suita ble materials include hydroquinone or derivatives thereof, 0- and p-aminophenols, p-methylaminophenyl sulfate, p-hydroxyphenylglycine, oand pphenylenediamine, l-phenyl-3- pyrazolidone, and alkali and alkaline earth metal oxalates and formates. The oxidizing and reducing components of the image-forming material may be combined in a single solution or one or both components may be incorporated in the photosensitive layer or in separate layers in the copy medium, applied as separate solutions to the exposed copy medium. Exemplary of the multilayer systems to which the invention described herein is applicable are US. Pat. Nos. 3,152,903 and 3,429,706.

Additionally, the image-forming materials or physicaldevelopers may contain organic acids or alkali metal salts thereof, which can react with metal ions to form complex metal ions. Further, the developers may contain other complexing agents and the like to improve image formation and other properties found to be desirable to the art.

Following contact of the exposed copy medium with the developer, there is a visible metallic image in the exposed areas of the copy medium andmetallic ions in the unexposed areas. The copy medium is then contacted with an organic mercaptan compound. This compound must be selected so as to be capable of going into solution to react with the metal ions in the unexposed portions of the copy medium to form metal mercaptide salts insoluble in a photographic bleaching solution. In addition, the mercaptan compound should not affect the metallic image in the exposed portions of the copy medium. It should be obvious that the selection of the organic mercaptan compound is therefore dependent upon the specific metal used to form the visible image, the bleaching solution used and other factors obvious to those skilled in the art. Preferred mercaptans are the heterocyclic mercaptan compounds corresponding to the formula:

where Z represents the atoms necessary to complete the heterocyclic ring containing preferably a total of five atoms and -SX is the mercapto group where X is a cation such as hydrogen, an alkali metal such as sodium or potassium, ammonium or an organic amine residue of such an amine as triethylaminc, triethanolamine, morpholinc, and the like. In addition, many of the heterocyclic mercaptan compounds can be in the tautomeric form, for example, in the thione form, in which case the labile hydrogen atom in the mercapto group becomes bonded to the nitrogen atom and the group becomes a thiocarbonyl C S) group.

Any of the heterocyclic compounds which contain at least one nitrogen atom and a mercapto'group as described above, are preferred. However, particularly good results are obtained with mercatotetrazoles, especially the five-mercaptotetrazoles as represented by the following formula:

l sx

where SX is as defined above and R is an aliphatic or aromatic substituent such as, for example, alkoxy, phenoxy, halo, cyano, nitro, amino, substituted amino, sulfo, sulfonyl, substituted sulfonyl, sulfonylphenyl, sulfonylalkyl, sulfonylaminophenyl, carboxy, carboxylates, and the like. Some specific heterocyclic compounds are, for example, Z-mercapto-S-phenyl-l ,3,4,-oxadiazole, 2-mercapto-5-methyl-l ,3,4- thiadiazine, Z-mercaptobenzoxazole, 3-mercapto-1,2,4- triazole, l-rnethyl-2-mercaptoimidazole, 2-amino-5-mercaptol ,3,4-thiadiazole, l-phenyl-5-mercaptotetrazole, Z-mercaptobenzimidazole, 4'phenyliminothiourazole, Z-mercaptothiazoline, 5-methyloxazoline-2-thiol, 2-mercaptobenzothiazole, and S-mercapto-l -phenyl-1 ,2,3,4-tetrazole.

Other preferred organic mercapto compounds include aromatic, aliphatic and heterocyclic compounds containing the SX radical and at least one additional water-solubilizing radical, such as a radical from the group consisting of halo, cyano, nitro, amino, carboxyl, sulfonyl, and the like. An especially preferred compound is thiourea.

The next step in the reversal process comprises contact of the copy medium with a photographic bleaching solution; Such bleaching solutions are well known in the art and taught, for example, in Glafkides, Photographic chemistry, Volume I, Fountain Press, London (1960), page 178, et seq. Aqueous solutions of cupric chloride, ferric chloride, and cupric sulfate are preferred. The bleaching solution reoxidizes the metallic image in the exposed portions of the copy medium soluble salts without affecting the metallic-mercaptide salts in the nonexposed areas of the copy medium.

The final step in the reversal process comprises contacting the copy medium with a conventional photographic fixing agent to dissolve and remove the soluble metal salts from the exposed portions of the copy medium. Typical fixing solutions are taught by Neblette, Photography Its Materials and Processes, D. Van Nostrand Company, Incorporated, New York (1952), pages 224 to 233. Thiosulfates are preferred for purposes of the present invention.

Upon completion of the process, a positive image in the nonexposed areas of the copy medium is obtain. The image has excellent contrast. It is believed that the contrast is due to a number of factors including the coloration of the mercaptide salts, a possible buildup of metal ions on the mercaptide salt from the bleaching solution, reduction of white titanium dioxide to black titanium dioxide where titanium dioxide is used as a photoconductor, and a possible buildup of silver from dissolved silver salts.

The reversal process described above is also useful for a copy medium comprising a silver halide emulsion. In this em bodiment of the invention, an exposed silver halide emulsion would be developed with a known photographic developing agent such as those described above, and preferably containing a small quantity of a silver halide solvent such as thiosulfate, contacted with a mercaptan to form the silvermercaptan salt in the nonexposed areas of the copy medium, contacted with a photographic bleaching solution to oxidile metallic silver in the exposed portions of the copy medium to soluble salts, and finally, contacted with a fixing agent to dissolve the soluble silver salts from the exposed portions of the copy medium leaving the silver mercaptide salts behind as a positive image in the nonexposed areas of the copy medium.

In each of the embodiments described above, the process may be modified by incorporation of the organic mercaptan compound into the binder layer of the copy medium. By modifying the process in this manner, the overall reversal processing time is decreased by the avoidance of the step of contacting the developed copy medium with the organic mercaptan compound.

If a copy medium is used having a binder a separate layer that is a heat-sensitive composition which forms an oleophilichydrophilic image pattern upon selective imagewise application of heat, the reversal process of this invention can be utilized for the formation of planographic printing plates by addition of the subsequent step of uniformly exposing the developed positive image to heat thereby causing selective heating in the image areas producing an oleophilic-hydrophilic image pattern. This oleophilic-hydrophilic image bearing printing plate may be used with a polar solvent-based ink or a greasy or oil-based ink as a printing master. The formation of planographic printing plates using a heat-sensitive composition which forms an oleophilic-hydrophilic image pattern upon exposure to heat is disclosed in commonly-owned US. Pat. application Ser. No. 675,798 in the name of E. Berman, now abandoned.

The heat-sensitive composition is one which forms an oleophilic-hydrophilic image pattern upon selected imagewise application of heat. The heat-sensitive composition is a multiphase system comprising a high-melting continuous phase and a low-melting dispersed phase. By selectively applying heat to the heat-sensitive layer so that the dispersed phase melts and the high-melting continuous phase does not melt, an image pattern corresponding to the dispersed phase will be formed on the surface of the continuous phase. Therefore a hydrophilic continuous phase-with an oleophilic dispersed phase produces an oleophilic image pattern corresponding to those areas which have been heated to a temperature between the melting point of the dispersed phase and the continuous phase. When the heat-sensitive composition comprises an oleophilic continuous phase and a hydrophilic dispersed phase, a hydrophilic image pattern is produced in those areas which are selectively heat imaged to a temperature between the melting point of the dispersed phase and the continuous phase. A preferred heat-sensitive composition comprises a polyphase system having a hydrophilic film-form colloid as the continuous phase and adispersed phase of oleophilic waterrepellent particles which form an oleophilic image on a planographic surface when released to the surface of the coating from the polyphase system in the heat-imaged areas. Preferably, the continuous phase comprises a water-permeable hydrophilic film-forming colloid. The dispersed phase preferably comprises a finely divided high molecular weight oleophilic polymer. Preferably this oleophilic polymer is in the form of latex particles which form a fragile, water-receptive and greasy-ink repellent film when deposited as a dried thin layer of latex and which is rendered water repellent and greasy-ink receptive when heating to a temperature between about 35 C. and 235 C.

Specific examples of suitable heat-sensitive compositions comprising a hydrophilic continuous phase and an oleophilic dispersed phase are disclosed in Belgian Pat. specification No. 656,713 incorporated herein by reference.

The hydrophilic materials useful in the heat-sensitive composition include, for example, polyvinyl alcohol, ethyl cellulose, carboxymethyl cellulose, casein, gelatin, sodium alginate, water-soluble vegetable gums, such as guar gum, synthetic polymers, such as sodium or ammonium polyacrylate, and many other water-soluble hydrophilic film-forming colloids or colloidal agglutinates.

These hydrophilic materials may be insolubilized in order to improve their durability as a planographic plate surface by methods known to the art. For example, gelatin may be hardened by the addition of formaldehyde, polyvinyl alcohol is effectively insolubilized by dimethylolurea incorporated in the formulation, and sodium alginate or sodium polyacrylate may be effectively treated with a solution of zinc chloride applied over the dried coating.

Oleophilic materials useful in the heat-sensitive composition include many of the materials listed above as suitable binders and include synthetic polymers such as polyethylene, polystyrene, polymethylmethacrylate, polyvinyl chloride, polyacrylonitrile, poly(N-vinylcarbazole), and the like. These oleophilic, hydrophobic polymers are preferably used in the form of latexes. When the dispersed phase of a heat-sensitive composition comprises latex particles, these are generally surrounded by wetting or dispersing agents. It is believed that the wetting or dispersing agent provides a heat-sensitive composition which is especially suitable for allowing the image-forming materials to properly permeate the surface of the planographic printing plate, thereby providing excellent development of the latent images produced by exposure of the photoconductor layer. Additional materials which may be suitable for the oleophilic-hydrophobic phase of the heat-sensitive composition are the oils or the waxes such as the vegetable, mineral, insect, petroleum, animal and synthetic waxes.

The ratio of the continuous phase of the heat-sensitive composition to the dispersed phase of said composition will vary according to the nature of the continuous phase, the nature of the dispersed phase, the nature of the ink being used and like factors known to the art. in general, however, the ratio of the dispersed phase in respect to the continuous phase should preferably be in excess of 1:1 and more preferably in excess of 3:2.

The heat-sensitive composition may be used in a separate layer from the photoconductor layer or it may be in the form of a mixture combining the photoconductor and the heat-sensitive composition in one layer. On the other hand, the multiphase heat-sensitive composition may also, in the alternative, be separated into separate layers. For example, the hydrophilic continuous phase may form a separate layer on top of an oleophilic layer.

The heat-producing radiation includes any type of radiation which upon exposure to a dark or visible surface will cause heating. For example, this would include infrared radiation or any electromagnetic radiation in a visible spectrum. The intensity and duration of the integral or nondifferential light exposure are such that the surface of the recording layer is struck by a light energy of at least 0.01 watt-seconds/crnF. To reduce lateral conduction of heat within the recording material, the nondifferential exposure is preferably very short. The exposure is preferably not more than 10 second in duration and even more preferably, less than 10" second and the best results are obtained between l0 and 10 seconds. Such exposures require high-energy radiation sources and preferably ones wherein the surface recording layer is struck by light energy of at least 0.1 wattseconds/cm. To obtain exposure times between 10' and 10 seconds, it is generally desirable to use high-energy radiation sources such as flash lamps. Gas discharge lamps which emit light in the wavelength ranges from about 0.3 micron to about 1 micron are especially desirable.

EXAMPLE 1 A paper support is coated with a finely divided titanium dioxide dispersed in a gelatin binder. After drying, the copying medium thus produced is exposed to an image pattern from an ultraviolet light source for one to two seconds duration, thereby giving an exposure of 400-meter-candle seconds and producing a latent image on the copy medium.

The thus-exposed copy medium is then immersed for about one-half second in an aqueous solution of 0.40 molar silver nitrate followed by immersion for about one-half second in an aqueous developing solution comprising Metol (pmethylaminophenyl sulfate) to form a visible negative silver image in the exposed portion of the copy medium. Thereafter, the copy medium is immersed for about 1 second in an aqueous solution of about 1 percent by weight of the potassium salt of l-phenyl-5-mercaptotetrazole followed by a l-second immersion in an aqueous solution of 2.0 molar cupric chloride. Finally, the copy medium is immersed in a sodium thiosulfate fixing bath. The positive image so formed is excellently sharp and of good density.

EXAMPLE 2 A polyethylene terephthalate support is coated with a finely divided titanium dioxide dispersed in a gelatin-polyethylene composition comprising:

10 percent aqueous solution of gelatin, 20 milliliters;

40 percent aqueous dispersion of polyethylene having a particle size of 0.1 micron and an average molecular weight of 30,000, 10 milliliters;

3 percent aqueous solution of formaldehyde, 6/ l0 milliliter.

After drying, the copy medium so formed is developed to a positive image following the procedures and compositions of Example 1. Thereafter, the thus-developed copy medium is irradiated with an infrared radiation source in a thermographic copying machine. The image areas of the copy medium are heated and thereby converted from a hydrophilic to an oleophilic-hydrophobic surface. The nonimage areas of the copy medium remain hydrophilic. An oil-base ink is used with the copy medium to produce a positive copy of the original. A polar solvent based ink is used with the copy medium as a master for producing negative copies of the original.

EXAMPLE 3 The procedure of Example 1 is repeated with the substitution of an aqueous solution of 2-mercaptothiazoline for the solution of the potassium salt of 1-phenyl-5-mercaptotetrazole with comparable results.

EXAMPLE 4 A photographic paper coated with a silver halide emulsion is given normal exposure to a step wedge. It is then developed in a developer of the following composition:

Metal 20 grams Sodium sulfite 20 grams Sodium thiocyanate 1 gram Citric acid 10 grams Water to l liter of solution Contact of the exposed copy medium with the above solution results in a visible silver image in the exposed portions of the copy medium. Thereafter, the copy medium is immersed in a 1 percent aqueous solution of 5-mercapto-3-phenyl-1 ,3,4- thiadiazole-Z-thione followed by immersion in a solution of two-molar ferric chloride. Thereafter, the copy medium is immersed in a fixing solution of sodium thiosulfate.

EXAMPLE 5 The procedure of Example 4 is repeated except that the copy medium is coated with a gelatin-polyethylene composition of the proportions and composition of Example 2. This copy medium is then processed according to the procedure of Example 4 and irradiated with an infrared radiation source in a thermographic copying machine. The image areas of the copy medium are heated and thereby converted from a hydrophilic to an oleophilic-hydrophobic surface. The nonimage areas of the copy medium remain hydrophilic. An oil base ink may be used with the copy medium to produce a positive copy of the original. A polar solvent base ink may be used with the copy medium as a master for producing negative copies of the original.

We claim:

1. A photographic reversal process for developing a positive photographic image of an original comprising the steps of (a) exposing a photosensitive copy medium comprising a photoconductor imagewise to provide a latent negative image, (b) contacting the copy medium with a developer comprising a solution of metal ions to provide a metallic image in the exposed portions of the medium, (c) contacting the copy medium with an organic mercaptan compound that forms insoluble metal-mercaptide salts in the nonexposed areas of the copy medium, d) contacting the copy medium with a photographic bleaching solution which reoxidizes the metallic image in the exposed portions of the copy medium to soluble salts and (e) contacting the copy medium with a photographic fixing solution to dissolve the soluble salts from the exposed portions of the medium thereby providing a positive photographic image.

2. The process of claim 1 where the organic mercaptan compound is a heterocyclic compound corresponding to the formula:

where Z represents the atoms necessary to complete the heterocyclic ring and -SX is the mercapto group where X is a cation selected from the group consisting of hydrogen, alkali metal, ammonium and an organic amine residue.

3. The process of claim 2 where the heterocyclic ring of the organic mercaptan is a five-membered ring.

4. The process of claim 2 where the organic mercaptan corrcnpnudn tn the following formula:

N=N-R l l X where R is a radical selected from the group of aliphatic and aryl.

6. The process of claim 2 where the organic mercaptan is lphenyl-S-mercaptotetrazole.

7. The process of claim 2 where the organic mercaptan is a member selected from the group consisting of aromatic mercaptans, aliphatic mercaptans and heterocyclic mercaptans.

8. The process of claim 7 where the organic mercaptan contains a water-solubilizing group.

9. The process of claim 2 where the organic mercaptan is applied to the photosensitive copy medium in aqueous solution.

10. The process of claim 1 where the developed negative metallic image in the exposed portions of the copy medium is a silver image.

11. The process of claim 1 where the photographic bleaching solution is an aqueous solution comprising an inor ganic salt selected from the group consisting of cupric chloride, ferric chloride, and cupric sulphate.

12. The process of claim 1 where the photographic bleaching solution is an aqueous two-molar cupric chloride solution.

13. The process of claim 1 where the photographic fixing solution comprises an aqueous solution of a thiosulphate.

14. The process of claim 1 where the photosensitive copy medium comprises a silver halide emulsion.

15. The process of claim 14 where the photographic copy medium is developed by contacting the medium with a developer comprising a reducing agent for silver and a silver halide solvent.

16. The process of claim 1 where the copy medium comprises an inorganic photoconductor.

17. The process of claim 16 where the inorganic photoconductor is a metal oxide.

18. The process of claim 16 where the inorganic photoconductor is titanium dioxide.

19. The process of claim 16 where the copy medium is developed by contact with a solution of a reducible metal ion having the oxidizing power or at least cupric ion followed by contact with a solution of a reducing agent therefor.

20. The process of claim 19 where the reducible metal ion is the silver ion.

21. The process of claim 1 where the photosensitive copy medium comprises a photosensitive material and heat-sensitive composition comprising a hydrophilic continuous phase and an oleophilic dispersed phase which forms an oleophilichydrophilic image pattern upon selective imagewise application of heat.

22. The process of claim 21 including a final step of heating the photosensitive copying medium to a temperature of between about 35 C. and 235 C., thereby producing a planegraphic printing master having an oleophilic-hydrophilic image pattern.

23. The process of claim 22 where the heat-sensitive composition forms a normally hydrophilic planographic surface of said copy medium and comprises particles of oleophilic, water-repellent particles dispersed within a continuous phase of a hydrophilic binder and forms an oleophilic image on a planographic surface at areas subjected to said imagewise application of heat.

24. The process of claim 21 where the heat-sensitive composition is a binder for the photosensitive material of the photosensitive copy medium.

25. The process of claim 21 where the heat-sensitive composition is a separate layer displaced over a layer of photosensitive material of the photosensitive copy medium.

26. A photographic reversal process for developing a positive photographic print of an original comprising the steps of (a) exposing a copy medium comprising a photoconductor imagewise to a source of radiation to provide a latent negative image (b) contacting the copy medium with a developer comprising a first solution of reducible metal ions having at least the oxidizing power of the cupric ion and a second solution comprising a reducing agent for said metal ions to provide a negative metallic image in the exposed portions of the copy medium, (c) contacting the copy medium with an organic mercaptan compound that forms insoluble metal-mercaptide salts in the nonexposed areas of the copy medium, (d) contacting the copy medium with a photographic bleaching solution which reoxidizes the metallic image in the exposed portions of the copy medium to soluble salts and (e) contacting the copy medium with a photographic fixing solution to dissolve the soluble salts from the exposed portions of the copy medium thereby providing a positive photographic image.

27. The process of claim 26 where the organic mercaptan compound is a heterocyclic mercaptan compound corresponding to the formula:

where Z represents the atoms necessary to complete the heterocyclic ring and SX is the mercapto group where X is a cation selected from the group consisting of hydrogen, alkali metal, ammonium and an organic amine residue.

28. The process of claim 27 where the organic mercaptan compound corresponds to the formula:

where R is a radical selected from the group of aryl and aliphatic.

29. The process of claim 27 where the mercaptan is l-phenyI-S-mercaptotetrazole.

30. The process of claim 26 where the developer for the copy medium comprises an aqueous solution of silver ions and a second solution of a reducing agent therefore.

31. The process of claim 26 where the copy medium comprises a photoconductor and a heat-sensitive composition comprising a hydrophilic continuous phase and an oleophilic dispersed phase which forms an oleophilic-hydrophilic image pattern upon selective imagewise application of heat.

32. The process of claim 31 including a final step of heating the copy medium to a temperature of between about 35 and 235 C. to produce a planographic printing master having an oleophilic-hydrophilic image pattern.

33. A photographic reversal process for developing a positive photographic print of an original comprising the steps of (a) exposing a silver halide copy medium imagewise to a source of radiation to provide a latent negative image (b) contacting the copy medium with a silver halide developer to provide a negative silver image in the exposed portions of the copy medium, (c) contacting the copy medium with an organic mercaptan compound that forms insoluble silver-mercaptide salts in the nonexposed areas of the copy medium, (d) contacting the copy medium with a photographic bleaching solution which reoxidizes the silver image in the exposed portions of the copy medium to soluble salts and (e) contacting the copy medium with a photographic fixing solution to dissolve the soluble silver salts from the exposed portions of the copy medium thereby providing a positive photographic image.

34. The process of claim 33 where the organic mercaptan compound is a heterocyclic mercaptan compound corresponding to the formula:

I Z I I= .'osx where Z represents the atoms necessary to complete the heterocyclic ring and SX is the mercapto group where X is a cation selected from the group consisting of hydrogen, alkali metal, ammonium and an organic amine residue.

35. The process of claim 34 where the organic mercaptan compound corresponds to the formula:

where R is a radical selected from the group of aryl and aliphatic.

36. The process of claim 35 where the mercaptan is l-phenyl-S-mercaptotetrazole.

37. The process of claim 33 where the copy medium comprises a photoconductor and a heat-sensitive composition comprising a hydrophilic continuous phase and an oleophilic dispersed phase which forms an oleophilic-hydrophilic image pattern upon selected imagewise application of heat.

38. The process of claim 37 including a final step of heating the copy medium to a temperature of between about 35 and 235 C. to produce a planographic printing master having an oleophilic-hydrophilic image pattern.

39. A photographic reversal process comprising the steps of (a) contacting a copy medium comprising a metal image pattern and a metal ion image pattern with an organic mercaptan compound to form insoluble metal mercaptide salts in the areas corresponding to the metal ion image pattern, and (b) contacting the copy medium with a photographic bleaching agent to oxidize the metallic image. I

40. A process as in claim 39 wherein the copy medium comprising a metal image pattern and a metal ion image pattern is formed by exposing and developing by contacting with a solution of metal ions a copy medium comprising a photosensitive material capable of producing a physically developable image.

41. A process as in claim 40 wherein the photosensitive material is at least one member selected from the group consisting of a reversibly activatable photoconductor, a silver halide, and aromatic diazosulfonate, and o-hydroxybenzenediazonium compounds, and o-hydroxynaphthalene diazonium compound, and aromatic diazocyanide, and 0- or p-nitro-mandelo nitrile, a bisulfite compound of 0- or pnitrobenzaldehyde, inorganic complex compounds from which one or more ions or molecules are liberated upon exposure, and ferric compounds.

42. The process as in claim 40 where the organic mercaptan compound is a heterocyclic compound corresponding to the formula:

where Z represents the atoms necessary to complete the heterocyclic ring and --SX is the mercapto group where X is a cation selected from the group consisting of hydrogen, alkali metal, ammonium and an organic amine residue.

43. The process as in claim 42 where the heterocyclic ring of the organic mercaptan is a five-membered ring.

44. The process of claim 42 where the organic mercaptan corresponds to the following formula: 

2. The process of claim 1 where the organic mercaptan compound is a heterocyclic compound corresponding to the formula: where Z represents the atoms necessary to complete the heterocyclic ring and -SX is the mercapto group where X is a cation selected from the group consisting of hydrogen, alkali metal, ammonium and an organic amine residue.
 3. The process of claim 2 where the heterocyclic ring of the organic mercaptan is a five-membered ring.
 4. The process of claim 2 where the organic mercaptan corresponds to the following formula: where R is a radical selected from the group of aliphatic and aryl.
 5. The process of claim 2 where the organic mercaptan is selected from the group consisting of 2-mercapto-5-phenyl-1,3,4,-oxadiazole, 2-mercapto-5-methyl-1,3,4-thiadiazine, 2-mercaptobenzoxazole, 3-mercapto-1,2,4-triazole, 1-methyl-2-mercaptoimidazole, 2-amino-5-mercapto-1,3,4-thiadiazole, 1-phenyl-5-mercaptotetrazole, 2-mercaptobenzimidazole, 4-phenyliminothiourazole, 2-mercaptothiazoline, 5-methyloxazoline-2-thiol, 2-mercaptobenzothiazole, and 5-mercapto-1-phenyl-1,2,3, 4-tetrazole.
 6. The process of claim 2 where the organic mercaptan is 1-PHENYL-5-mercaptotetrazole.
 7. The process of claim 2 where the organic mercaptan is a member selected from the group consisting of aromatic mercaptans, aliphatic mercaptans and heterocyclic mercaptans.
 8. The process of claim 7 where the organic mercaptan contains a water-solubilizing group.
 9. The process of claim 2 where the organic mercaptan is applied to the photosensitive copy medium in aqueous solution.
 10. The process of claim 1 where the developed negative metallic image in the exposed portions of the copy medium is a silver image.
 11. The process of claim 1 where the photographic bleaching solution is an aqueous solution comprising an inorganic salt selected from the group consisting of cupric chloride, ferric chloride, and cupric sulphate.
 12. The process of claim 1 where the photographic bleaching solution is an aqueous two-molar cupric chloride solution.
 13. The process of claim 1 where the photographic fixing solution comprises an aqueous solution of a thiosulphate.
 14. The process of claim 1 where the photosensitive copy medium comprises a silver halide emulsion.
 15. The process of claim 14 where the photographic copy medium is developed by contacting the medium with a developer comprising a reducing agent for silver and a silver halide solvent.
 16. The process of claim 1 where the copy medium comprises an inorganic photoconductor.
 17. The process of claim 16 where the inorganic photoconductor is a metal oxide.
 18. The process of claim 16 where the inorganic photoconductor is titanium dioxide.
 19. The process of claim 16 where the copy medium is developed by contact with a solution of a reducible metal ion having the oxidizing power or at least cupric ion followed by contact with a solution of a reducing agent therefor.
 20. The process of claim 19 where the reducible metal ion is the silver ion.
 21. The process of claim 1 where the photosensitive copy medium comprises a photosensitive material and heat-sensitive composition comprising a hydrophilic continuous phase and an oleophilic dispersed phase which forms an oleophilic-hydrophilic image pattern upon selective imagewise application of heat.
 22. The process of claim 21 including a final step of heating the photosensitive copying medium to a temperature of between about 35* C. and 235* C. thereby producing a planographic printing master having an oleophilic-hydrophilic image pattern.
 23. The process of claim 22 where the heat-sensitive composition forms a normally hydrophilic planographic surface of said copy medium and comprises particles of oleophilic, water-repellent particles dispersed within a continuous phase of a hydrophilic binder and forms an oleophilic image on a planographic surface at areas subjected to said imagewise application of heat.
 24. The process of claim 21 where the heat-sensitive composition is a binder for the photosensitive material of the photosensitive copy medium.
 25. The process of claim 21 where the heat-sensitive composition is a separate layer displaced over a layer of photosensitive material of the photosensitive copy medium.
 26. A photographic reversal process for developing a positive photographic print of an original comprising the steps of (a) exposing a copy medium comprising a photoconductor imagewise to a source of radiation to provide a latent negative image (b) contacting the copy medium with a developer comprising a first solution of reducible metal ions having at least the oxidizing power of the cupric ion and a second solution comprising a reducing agent for said metal ions to provide a negative metallic image in the exposed portions of the copy medium, (c) contacting the copy medium with an organic mercaptan compound that forms insoluble metal-mercaptide salts in the nonexposed areas of the copy medium, (d) contacting the copy medium with a photographic bleaching solution which reoxidizes the metallic image in the exposed portions of the copy medium to soluble salTs and (e) contacting the copy medium with a photographic fixing solution to dissolve the soluble salts from the exposed portions of the copy medium thereby providing a positive photographic image.
 27. The process of claim 26 where the organic mercaptan compound is a heterocyclic mercaptan compound corresponding to the formula: where Z represents the atoms necessary to complete the heterocyclic ring and -SX is the mercapto group where X is a cation selected from the group consisting of hydrogen, alkali metal, ammonium and an organic amine residue.
 28. The process of claim 27 where the organic mercaptan compound corresponds to the formula: where R is a radical selected from the group of aryl and aliphatic.
 29. The process of claim 27 where the mercaptan is 1-phenyl-5-mercaptotetrazole.
 30. The process of claim 26 where the developer for the copy medium comprises an aqueous solution of silver ions and a second solution of a reducing agent therefore.
 31. The process of claim 26 where the copy medium comprises a photoconductor and a heat-sensitive composition comprising a hydrophilic continuous phase and an oleophilic dispersed phase which forms an oleophilic-hydrophilic image pattern upon selective imagewise application of heat.
 32. The process of claim 31 including a final step of heating the copy medium to a temperature of between about 35* and 235* C. to produce a planographic printing master having an oleophilic-hydrophilic image pattern.
 33. A photographic reversal process for developing a positive photographic print of an original comprising the steps of (a) exposing a silver halide copy medium imagewise to a source of radiation to provide a latent negative image (b) contacting the copy medium with a silver halide developer to provide a negative silver image in the exposed portions of the copy medium, (c) contacting the copy medium with an organic mercaptan compound that forms insoluble silver-mercaptide salts in the nonexposed areas of the copy medium, (d) contacting the copy medium with a photographic bleaching solution which reoxidizes the silver image in the exposed portions of the copy medium to soluble salts and (e) contacting the copy medium with a photographic fixing solution to dissolve the soluble silver salts from the exposed portions of the copy medium thereby providing a positive photographic image.
 34. The process of claim 33 where the organic mercaptan compound is a heterocyclic mercaptan compound corresponding to the formula: where Z represents the atoms necessary to complete the heterocyclic ring and -SX is the mercapto group where X is a cation selected from the group consisting of hydrogen, alkali metal, ammonium and an organic amine residue.
 35. The process of claim 34 where the organic mercaptan compound corresponds to the formula: where R is a radical selected from the group of aryl and aliphatic.
 36. The process of claim 35 where the mercaptan is 1-phenyl-5-mercaptotetrazole.
 37. The process of claim 33 where the copy medium comprises a photoconductor and a heat-sensitive composition comprising a hydrophilic continuous phase and an oleophilic dispersed phase which forms an oleophilic-hydrophilic image pattern upon selected imagewise application of heat.
 38. The process of claim 37 including a final step of heating the copy medium to a temperature of between about 35* and 235* C. to produce a planographic printing master having an oleophilic-hydrophilic image pattern.
 39. A photographic reversal process comprising the steps of (a) contacting a copy medium comprising a metal image pattern and a metal ion image pattern with an organic mercaptan compound to form insoluble metal mercaptide salts in the areas corresponding to the metal ion image pattern, and (b) contacting the copY medium with a photographic bleaching agent to oxidize the metallic image.
 40. A process as in claim 39 wherein the copy medium comprising a metal image pattern and a metal ion image pattern is formed by exposing and developing by contacting with a solution of metal ions a copy medium comprising a photosensitive material capable of producing a physically developable image.
 41. A process as in claim 40 wherein the photosensitive material is at least one member selected from the group consisting of a reversibly activatable photoconductor, a silver halide, and aromatic diazosulfonate, and o-hydroxybenzenediazonium compounds, and o-hydroxynaphthalene diazonium compound, and aromatic diazocyanide, and o- or p-nitro-mandelo nitrile, a bisulfite compound of o- or p-nitrobenzaldehyde, inorganic complex compounds from which one or more ions or molecules are liberated upon exposure, and ferric compounds.
 42. The process as in claim 40 where the organic mercaptan compound is a heterocyclic compound corresponding to the formula: where Z represents the atoms necessary to complete the heterocyclic ring and -SX is the mercapto group where X is a cation selected from the group consisting of hydrogen, alkali metal, ammonium and an organic amine residue.
 43. The process as in claim 42 where the heterocyclic ring of the organic mercaptan is a five-membered ring.
 44. The process of claim 42 where the organic mercaptan corresponds to the following formula: where R is a radical selected from the group of aliphatic and aryl.
 45. The process of claim 42 where the organic mercaptan is 1-phenyl-5-mercaptotetrazole.
 46. The process of claim 39 where the photographic bleaching solution is an aqueous two-molar cupric chloride solution.
 47. The process of claim 39 where the process copy medium is contacted with a photographic fixing or stabilizing agent. 